Add ability to use coupons for events

I would like to be able to have a field that is a "coupon" code. It will affect the cost of the event by what is configured with the coupons. I'd like to be able to offer single-use per user or where it is a valid coupon if the offer is still valid / published. Maybe even to be able to offer "# of uses" per user of a coupon code for registering to events. or, to offer the ability to do "for the next 10 users" type coupons. If you can get started with single-use per user and a valid coupon for unlimited usage while published, that would be a great start!